Dynamic Propeller Balancing Using the Model 1015 ProBalancer Sport Product Support ACES Systems/TEC Aviation Division.

Dynamic Propeller Balancing

Using the Model 1015 ProBalancer Sport

Product Support ACES Systems/TEC Aviation Division

Goals for This Training

• Understand Basics of Vibration• Understand the Benefits of Balancing • Understand the Fundamentals for using the

ProBalancer Sport for Dynamic Propeller Balancing

Overview

• The Basics of Vibration– Definition – Why it happens– How the ProBalancer Sport measures it– How we correct it

• Vibration is defined as:– “mechanical oscillation about an equilibrium

point.”• For the purpose of Propeller Balance,

vibration can be described as:– “the unwanted, unproductive, cyclic oscillation

of the propeller and engine assembly about its rotational axis.”

The Basics of Vibration

Definition

• All noise and/or vibration is not generated by an imbalance in the propeller.

• To verify the vibration source, a vibration survey should be conducted and manufacturers’ limitations adhered to.


Remember


Why Does It Happen?

• When the weight of a rotating propeller and engine assembly is not equally distributed, the dominant or heavy point attempts to continue moving in a straight line. The resulting force attempts to pull the assembly outside its rotational axis. The assembly then orbits what would be the normal center of rotation, causing vibration.


Vibration-Related Complaints

• Cracked exhaust stacks and sheet metal• Higher than normal occurrence of engine and

prop oil leaks and light bulb failures• Physical movement of airframe (buzz in the seat,

yoke, rudder pedals)• Malfunctioning or failed avionics• Passenger complaints of noise in the cabin


Examples of the Effects of Vibration

• Vibration excites natural frequencies in other components throughout the airframe and engine assemblies.

• The expended energy from vibration causes wear of components, reduced performance, and passenger discomfort.


How the ProBalancer Sport Measures Vibration

• Sensor Type• Sensor Engineering

Unit• Characteristics of the

Sensor• Sensor Specifications• Sensor Mounting


How It Is Measured

• The vibration sensor generates a small voltage when the mass compresses the piezoelectric element. That voltage is proportional to the force being exerted on the element.


How It Is Measured

• Sensor Type– The ProBalancer Sport uses an accelerometer

to measures the rate of change of velocity with time.

• Engineering Unit – gs (equivalent gravities) - acceleration


How It Is Measured

• Sensor Characteristics– Accelerometers

• Measure Acceleration • Typically Reported in g’s• More Sensitive to Higher Frequencies• Directly Related to Force Caused by Unbalance• Used in Balancing (after conversion to velocity or

displacement)


How We Correct It

• Improve manufacturing methods• Remove and replace defective components• Static Balance• Static Balance + Dynamic Balance

Overview

• Understanding the Benefits of Balancing– The negative effects of vibration– How balancing effects service life and

economy of operation

The Benefits of Balancing

• Reduces:– Noise– Vibration– Airframe damage– Avionics damage– Fatigue and stress

on passengers

• Increases:– Economy of operation– Service life of airframe and components– Comfort

Overview

• Fundamentals for using the ProBalancer Sport for Dynamic Propeller Balancing– When to balance– Required equipment– Setting up the equipment– Data collection and processing– The balancing process– Avoiding the pitfalls

Fundamentals of Balancing

When to Balance

1.25 IPS

1.00 IPS

.50 IPS

.25 IPS

.15 IPS

.07 IPS0 IPS

Good - Not felt by occupants

Very Rough – Static balance recommended

Danger - Remove and Static

Slightly Rough - Balance for ride

Fair - Maximum after Dynamic

Rough – Dynamic balance recommended


When to BalanceAn example of a manufacturer’s balancing recommendation.• McCauley Service Letter 1989-4D

– Revised July 20, 2001– Endorses dynamic balance on propellers

installed on piston and turbine powered aircraft.

– Over 0.8 IPS initial reading - list of corrective actions.


When to BalanceAn example of a manufacturer’s balancing recommendation• Hartzell Service Letter HC-SL-61-165

– Revised December 7, 1995– Warns that all propellers need to be

inspected for abnormal grease leakage or vibration.

– Perform Troubleshooting and evaluate possible sources of vibration IAW engine/airframe mfr. instructions.


Equipment Required

• A device to collect vibration and phase data.

• A phase angle /speed sensing device

• A vibration sensing device

• Balance weights and hand tools.


Equipment Required

• Approved references– Airframe manual– Propeller Manual– Engine manual (in

some cases)– FAA-approved

“Guide to Propeller Balancing”


Equipment Required

• Make sure the approval letter is attached to the Guide and references the material being used (document number, date, revision, and change numbers if applicable.)


Equipment Required

AC20-37E Chapter 3 Paragraph 300.C.2.(d)

When approved aircraft or propeller manufacturer’s procedures are not available, there are other acceptable dynamic propeller balancing procedures. These include, but are not limited to… ACES Publication No. 100-OM-01, entitled “ACES Systems Guide to Propeller Balancing”. Dynamic balancing of propellers using FAA-approved or -accepted dynamic propeller balancing procedures is not considered a major propeller repair unless the propeller static balance weights are altered or when using… ACES type documents on propeller installations of 500 horsepower or more.

(emphasis added)


BEFORE Setting Up the Equipment

• Propeller Inspection Prior to Balancing

– Ensure all Airworthiness Directives have been accomplished for the propeller you are going to balance.

– Determine if there is a balancing procedure published by the airframe, engine or propeller manufacturer; if there is, it will take precedence.



– Inspect the propeller blades for damage, nicks etc. refer to FAA Advisory Circular 20-37E which outlines care of metal propellers, and to applicable propeller manufacturers maintenance requirements.

– If balancing composite propeller blades, refer to the propeller manufacturer's procedures for repair of the propeller.

– Inspect propeller assembly for proper installation and security.



– Perform a visual inspection of the spinner and spinner bulkhead for cracks, stop drills and welding. Mass trim weights MUST NOT be attached to a part with any of these conditions.

– To prevent an excessive number of weights from being attached to the spinner, remove any mass trim weights attached from previous dynamic balance jobs.

– Static balance weight attached to the propeller hub by a certified propeller shop MUST NOT be removed.



– Inspect your sensor and its attached cable for obvious damage, such as, chips, pinches, or cuts in the plastic on the cable, and dints or scratches on the sensor, etcetera.

– Inspect your tachometer and its attached cable for obvious damage, such as, chips, pinches, or cuts in the plastic on the cable, scratches on the tachometer lens, etcetera.

– Ensure the batteries in your analyzer have a sufficient charge to complete the balance job.


Setting Up the Equipment

• Always attach the vibration sensor as near as possible to the forward most point of the engine and as close to inline with the engine bearing as possible. The base of the sensor should always point to the center of the prop shaft.

• The vibration sensor should not be in line with a cylinder and should be positioned at 12:00 whenever possible.



• Attach the Phototach between 12 and 18 inches from the surface of the target blade and not perpendicular (90 degrees) to the surface of the blade. A 5 degree offset is best.

• The reflective tape should be a 2 inch long piece of 3M brand 7610, and not less than 1 inch wide. It should be installed no more than 14 inches out the prop blade from the center of the prop shaft.



• Cables should be routed away from rotating and high temp components. Secure with wire ties or tape to prevent excessive movement and possible damage.

• Do not close windows or doors on the cables as this may pinch or cut them. Make sure connections at the analyzer are secure.




Data Collection & Processing

• The vibration sensor is installed on the engine as near the front bearing as possible. The Phototach is mounted on the cowling, behind the propeller. The reflective tape is applied to the back side of the target propeller blade in line with the Phototach beam. The mass is the theoretical heavy spot in the propeller, and is located by correlating the “bump” from the vibration sensor and the amount of time that has passed since the Phototach signaled the passing of the reflective tape.



• The Reflective tape triggers a response as it passes the Phototach, which then sends an electrical signal to the analyzer.

• As the heavy spot on the propeller passes the vibration sensor, the sensor generates an electrical pulse and sends it to the analyzer.



• In this illustration, the vibration sensor and Phototach beam are co- located at the 12:00 or 0 degree position. Rotation is clock-wise from the viewers position. This is our starting point, elapsed time = 0



• The speed is 1 RPM. Fifteen seconds (90 degrees) of travel has occurred. In this sequence, the reflective tape has just entered the Phototach beam to trigger the tach event. Elapsed time = 15 seconds.



• In this sequence, the mass (heavy spot) is passing the accelerometer position, 15 seconds (90 degrees) after the tape passed the Phototach beam. Elapsed time = 30 seconds (180 degrees of travel).



• The tape and mass have both passed the 0 degree location. The unit now waits for the exact sequence to repeat for averaging. Elapsed time = 45 seconds (270 degrees of travel)





• The process is repeated while the analyzer averages out errors caused by momentary vibration events outside the running average.



• When sufficient data has been collected, the process is stopped by the analyzer and the averaged data displayed on screen.

• Notice that you have the option to Retake the data if desired.



• The analyzer will prompt you to shut down the engine.

• When less than 50 RPM are recognized by the analyzer, it will progress to the solution screen.



• A solution is then provided by the analyzer based on a temporarily stored influence coefficient or a calculated test weight.

• If required, the process is then repeated for refinement of the solution.

• Notice you have the option to split the weights between two angles if needed.


The Balancing Process

• With the equipment installed and all previously installed trim weights removed, head the airplane into the wind (10 KTS maximum) and begin the data collection.



• The analyzer will show a screen instructing you to warm the engine and advance your RPM to the designated balancing RPM.



• The analyzer will collect and average data until a sufficient amount of data samples have been collected. This should take between ten and thirty seconds under ideal conditions.



• When the sufficient data has need collected, the Review screen shows the averaged amplitude and the phase angle of the out of balance condition.



• The analyzer will prompt you to shut down. When a RPM reading of less than 50 RPM is indicated the analyzer will progress.



• After the analyzer detects the engines are shut down, it will suggest a balance solution.

• If you require a two hole solution select 1 for yes.



• If you split the weights, the analyzer will ask you for the angles of the two available holes.

• Enter the angles and press go.



• The analyzer screen will display its suggestion and ask you for the actual angle and weights you installed.

• This screen will repeat for each hole location, if you chose to split the weight.



• The start engine screen will be displayed again.

• The analyzer will repeat this balance process until the vibration has been driven below .07 IPS.



• Where to place the weights– Test weights can be placed under the spinner

retention screws. It may be necessary to use longer screws for the test weights. If doing so, account for the delta between the normal and the longer screw. Be sure you are measuring the angles in relation to the reflective tape.



Permanent weights may be installed under the flange or on the bulkhead. If installed under the flange, offset from spinner attaching screws by four times the diameter of the spinner screws.


The Balancing ProcessDO NOT use the spinner attachment screws for permanent weight applications. Apply an equal number of washers to each side of the bulkhead and compensate for the shortened arm when moving weight(s) to the spinner bulkhead.

Correction Calculation

• Diameter of spinner divided by 2 = radius of spinner (ex: 14 / 2 = 7.0”)

• Minus distance from test weight to permanent weight = permanent weight radius (ex: 7.0 - 1.5 = 5.5”)

• Required weight to balance x radius of spinner = net effect (ex: 25 g x 7.0 = 175 Gram inches)

• Divide by permanent weight radius = permanent weight (ex: 175 / 5.5 = 31.8 grams)


Avoiding the Pitfalls

• If you remove the spinner in order to remove previously installed trim weights, index it and make sure it is always reinstalled by the index mark. Check inside the spinner for foreign objects, excess grease and trapped water.



• Unstable or erratic RPM readings on the analyzer are most commonly caused by:– Angle of the Phototach relative to the tape.– Phototach outside the 18 inch maximum or

inside the 12 inch minimum distance.– Tape too narrow for the velocity of the prop.– Dirty or misaligned tape.– Defective Phototach or Cable.



• Unstable or erratic vibration amplitude readings on the analyzer are most commonly caused by:– Damaged or inoperative sensor– Pinched, Cut, or shorted cable– Unstable tachometer input.– Mechanical defects of the assembly being

balanced.



• You may also adjust the Phototach gain. Remove the screw holding the clear plastic cover on the aft end of the unit.



• The gain adjustment is the brass screw at the right. Make adjustment in a controlled environment such as with a bench grinder in a shop.



• Adjust the speed of the prop as closely as possible to the exact target RPM on EVERY run. A change in RPM will change the influence of an attached weight. Subsequent solutions will not have the same calculated results at different speeds.



• If an established influence for the engine and prop combination being balanced is not being used, the first weight the analyzer will ask you to install is a TEST weight. This weight may cause the vibration amplitude to increase. The intention of the test weight is only to induce a measurable change, not necessarily reduce the vibration.



• If the suggested TEST weight is greater than your experience tells you is necessary to induce a change, reduce the weight and enter the exact amount and angle of attachment into the analyzer. Remember that the amplitude may actually go up. This is not a malfunction of the equipment. Continue the balance process.



Test weight calculation.• Test Weight in Grams = ((Engine

Horsepower/10)+30)*IPS• g = (1000/10)+30)*1.0• g = (100+30)*1• g = 130



• There is no difference in the propeller balance procedure for a radial engine, opposed engine, turboprop, geared, variable pitch, or fixed pitch propeller.


Avoiding the Pitfalls• A variety of mechanical problems can show up at

propeller turning speed these include– Propeller out of track.– Crankshaft unbalance.

– Bearing problems.

– Loose or worn components in the engine.

– Defective crankshaft counterweights.

– Loose or worn components in the propeller hub.

– Loose airframe components.



• Some indications are:– Applying numerous (more than 3 or 4)

solutions without reducing the amplitude.– Phase angle changing radically between runs.– Phase angle that changes dramatically during

data acquisition. (At amplitudes below approximately .05 IPS this is not a defect.)



• In any of these cases, you will have little to no success with your balancing efforts. If you feel you are chasing the solution, check the equipment on another application before blaming your difficulties on the analyzer.

Dynamic Propeller Balancing Using the Model 1015 ProBalancer Sport Product Support ACES Systems/TEC Aviation Division.

Documents

effects of vibration

vibration survey

vibration source

basics of vibration

negative effects of

noise andor vibration

cabin slide

displacement slide